Download EVBUM2100 - 180-265 Vac up to 15 Watt Dimmable LED Driver

NCL30000LED2GEVB
180-265 Vac up to 15 Watt
Dimmable LED Driver
Evaluation Board
User's Manual
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EVAL BOARD USER’S MANUAL
Introduction
This manual also focuses on how the board can be
modified to support alternate output currents and power
levels. The NCL30000 datasheet contains additional
information on operation of the controller and LED driver
application. Application Note AND8451 details power
stage design details and AND8448 provides specific
information for dimming applications. Design calculations
are covered in greater detail in these documents.
The compact evaluation board is constructed with
through-hole components on the top and surface mount
components on the bottom side. This board was designed to
meet safety agency requirements but has not been evaluated
for compliance. When operating this board, observe
standard safe working practices. High voltages are present
on the board and caution should be exercised when handling
or probing various points to avoid personal injury or damage
to the unit.
Figures 1 and 2 show the top and bottom sides of this
evaluation board. AC input connects to the terminal block in
the upper left corner. Terminals are marked “L” and “N” for
Line and Neutral. The LED load connects to the terminal
block in the upper right corner. Note the board is labeled
“LED+” and “LED−“. Observe polarity when connecting
LED loads. Never connect LEDs to the driver while it is
running or before the output capacitors discharge after
removing input power. In open load conditions the output
capacitors charge to >56 volts. Energy stored in the output
capacitance can damage or shorten the effective life of the
LEDs if improperly discharged into the LEDs.
The NCL30000 is a power factor corrected LED driver
controller. This evaluation board manual describes the setup
and operation of the NCL30000LED2GEVB LED driver for
230 V input. The evaluation board implements an isolated
single stage Critical conduction Mode (CrM) flyback
converter providing a regulated constant current to an LED
load. This board has been specifically configured to support
leading and trailing edge line dimming and has been
characterized across a range of commercially available
dimmers. The output voltage range is suitable for nominal
4 to 15 high brightness power LEDs. Protection features
include open load protection, over temperature protection,
and overload limiting. As shipped, the evaluation board is
set up for the following parameters:
Evaluation Board Specifications
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Input Voltage Range: 180 − 265 Vac
Output Current: 350 mA 5%
Output Voltage Range: 12 − 50 Vdc
Output Power: up to 17.5 W
Full Load Efficiency: >82%
Power Factor: >0.93 Typical
50C Ambient Operation
Class B Conducted Emissions
Compatible with Triac and Electronic Dimmers
 Semiconductor Components Industries, LLC, 2012
September, 2012 − Rev. 2
1
Publication Order Number:
EVBUM2100/D
NCL30000LED2GEVB
Figure 1. Top Side of Board
Figure 2. Bottom Side of Board
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NCL30000LED2GEVB
Figure 3. Board Schematic
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NCL30000LED2GEVB
Board Configuration
On-time Capacitor
The evaluation board has been optimized for dimming
with a 12 W load. Output current is regulated at 350 mA
from 265 V rms down to a setpoint of about 200 V rms.
When the input voltage is ~200 V rms, the control method
changes from closed loop secondary side current control to
primary side control. As the input voltage is reduced further
the output current drops in a smooth fashion in response to
the lower input voltage. This response matches the driver to
a dimmer thus emulating the dimming response of an
incandescent bulb. The following information details
reconfiguring the evaluation board for alternate
applications.
The input voltage at which dimming or reduction of
output current occurs is controlled by C9, power delivered
to the LED load, and parameters from the evaluation board.
The approximate value of C9 is calculated by the formula
below:
C9 [
4 @ L pri @ P out @ I charge
hȀ @ V
2
pk @ V
Ctmax
@
ǒ
V pk
N @ V out
Ǔ
)1
(eq. 1)
Values in the equation above are described in Table 1
below:
Table 1. VARIABLES FOR CALCULATING CT CAPACITOR
Variable
Description
Lpri
Transformer Primary Inductance
Pout
Power Output to LEDs
Icharge
h’
Vpk
Vctmax
N
Vout
Value for Evaluation Board
0.00157
12
Nominal On Time Capacitor Charge Current
275 mA
Transformer/Secondary Efficiency
0.95
Dimming Point Peak Voltage
200 Vrms = 282.8 Vpk
Nominal On Time Capacitor Peak Voltage
4.93
Transformer Turns Ratio
3.83
LED Load Voltage (12 LEDs)
C9 [
37
4 @ 0.00157 @ 12 @ 275m
0.95 @ 282.8 2 @ 4.93
@
282.8 ) 1Ǔ + 166 pF
ǒ3.83
@ 37
(eq. 2)
Output Current Setup
In practice, the value of capacitance calculated is an
approximation of operating conditions and optimization is
required. Empirical testing with a dimmer may be done to
select the optimum input voltage for dimming to begin. A
value of 180 pF was selected for C9 on the evaluation board
to achieve desired results.
Modifying this evaluation board for alternate LED
configurations and power levels is straight forward. Using
the equation above, enter the target LED power, LED
voltage, and the target AC input voltage below which
dimming should occur. Select a capacitor somewhat below
the value returned by the approximate formula. Performance
should be evaluated using the desired dimmers. Check
operation by noting the conduction angle below which LED
current reduces. Increasing the value of capacitor C9 lowers
the conduction angle where dimming occurs. Performance
can be optimized by selecting the value of C9.
Figure 4 below is the bottom side of the evaluation board.
Component locations are circled indicating those values that
are most likely to be changed to optimize for a different
power level.
A particular driver application may require LED current
other than 350 mA. Output current is controlled by R29
located in Figure 4. The following formula is used to set the
output current.
R29 + 0.07
I out
(eq. 3)
Dissipation for current sense resistor R29 is defined by the
formula below.
P R29 + 0.07
R29
2
(eq. 4)
The secondary windings of power transformer T1 are
connected in series to support the 50 V/350 mA output
rating of the evaluation board. Applications below 25 V or
greater than 450 mA output should have the transformer
secondary windings configured in parallel. This helps
maintain proper primary bias voltage and enhances current
carrying capability of the transformer. Table 2 shows how to
configure the transformer flying leads in the PCB holes for
series and parallel configuration. Figure 5 is the top side of
the circuit board highlighting the wire holes H1 − H6.
Table 2. WINDING CONFIGURATION
Winding Configuration
H1
H2
H3
H4
H5
H6
Series (default)
FL1
<open>
FL2
FL3
<open>
FL4
Parallel
FL1
FL3
<open>
<open>
FL2
FL4
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NCL30000LED2GEVB
Figure 4. Bottom Side PCB Component Locations
Figure 5. PCB Holes for Transformer Leads
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NCL30000LED2GEVB
Primary Current Limit
As built, the evaluation board is suitable for 17.5 W
maximum. The transformer secondary windings will
support up to 1 A of LED current with secondary windings
configured in parallel.
A 300 V output rectifier was selected for applications up
to 50 Vdc output and 265 V ac input. Lower voltage
rectifiers are recommended for applications below 50 Vdc.
A lower forward voltage drop output rectifier will improve
efficiency. Selecting a rectifier with a higher current rating
typically provides lower forward drop at the currents of
interest. A 3 A rectifier was selected for the evaluation board
to provide low forward drop. Any change to the output
rectifier requires verifying the maximum voltage rating is
not exceeded.
Maximum current in the switching FET Q3 is established
by R20. The demo board components have been designed to
support up to 17.5 W output at 180 V rms input. Note C9 has
been preconfigured for 180 pF which limits the maximum
power. If the application requires alternate power level or
input voltage, the value of R20 can be adjusted. Lower
power or high input line voltage applications my benefit
from a higher value resistance which provides
cycle-by-cycle current monitoring in the event of a fault.
The formula below provides an estimated value for R20
which includes a 25% tolerance for components and start up
conditions.
R20 +
Output Capacitor
The evaluation board regulates constant current and
therefore the output voltage is determined by the LED load
characteristics at the set current level. Energy storage to
maintain high power factor and low output ripple current
requires relatively large output filter capacitors. The LED
load can be modeled as a constant voltage source with some
series impedance. In essence, the ripple current in the LEDs
is controlled by the series impedance coupling the constant
voltage nature of the filter capacitance and constant voltage
characteristic of the LEDs in a complex relationship.
Two 470 mF capacitors connected in parallel provide
about 30% or 105 mA peak-to-peak ripple for a 350 mA
average LED current. Increasing the output capacitance
reduces the ripple current and conversely decreasing
capacitance will increase the ripple. Applications requiring
average output currents other than 350 mA can be scaled to
this value. For example an application requiring 700 mA
requires two 1,000 mF capacitors in parallel to provide 30%
ripple.
0.5
1.25 @ I pri
(eq. 5)
Open Load Protection
The evaluation board includes a circuit to protect the
output capacitors in the event of open load conditions. The
output voltage will be limited when zener diode D12
exceeds the zener voltage plus ~0.7 V. D12 is presently 56 V
which means the maximum output will be approximately
56.7 V. D12 can be changed to protect output capacitors of
different voltage rating. Select D12 zener voltage to match
open load requirements. The location of D12 is shown in
Figure 4.
Typical Performance Data
Figure 6 below displays the relationship between input
voltage and LED current for a 12 LED, 13 W load. Higher
input voltages allow the secondary side control loop to
regulate 350 mA output current at 37 V nominal load. Note
the inflection point where reduction in current begins as the
input voltage is reduced below 200 Vac. This is the dimming
inception point.
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350
100%
315
90%
280
80%
245
70%
210
60%
175
50%
140
40%
105
30%
70
20%
LED Current
Efficiency
35
0
30
50
70
90
110
130
150
170
Input Voltage (Vac)
190
210
230
250
Efficiency
LED Current (mA)
NCL30000LED2GEVB
10%
0%
270
Figure 6. Line Regulation and Efficiency for 13 W Load
load at 230 Vac, 50 Hz input and applicable limits are shown
in Table 3.
Efficiency performance is shown in Figure 6 as well. Note
the efficiency remains above 70% until the output current
drops below 70 mA. The output voltage is about 34 V
meaning the delivered power is about 2.4 W or less than
20% of the full power. As the current delivered is reduced,
the fixed losses for startup and biasing begin to dominate the
efficiency curve resulting in a steep drop off of efficiency.
Harmonic content characterizes the waveshape of the
input current waveform. Odd order harmonics of the
fundamental distort the input waveform resulting in
non-sinusoidal shape. International standard IEC
61000−3−2 Class C places limits on input current harmonics
for lighting equipment. A category for devices drawing not
more than 25 W applies to this reference design.
Performance of this demonstration board with a 12 W LED
Table 3. INPUT CURRENT HARMONIC CONTENT
Harmonic
Value
Limit
3
11.02%
86%
5
5.16%
61%
Power factor and input current Total Harmonic Distortion
(THD) are performance factors receiving considerable
attention from utility companies and government agencies.
Figure 7 below displays performance of the evaluation
board. The EMI filter was designed for a 17.5 W load. The
filter can be optimized for higher power factor in
applications requiring less power.
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20
0.98
19
0.97
18
0.96
17
0.95
16
0.94
15
0.93
14
0.92
13
0.91
THD
Power Factor
12
0.9
11
10
Power Factor (PF)
Percent Input Current THD (%)
NCL30000LED2GEVB
0.89
180
195
210
225
Input Voltage (Vac)
240
0.88
270
255
Figure 7. Power Factor and THD
of greater than 10:1 was consistently demonstrated. Note
that minimum conduction angle and therefore LED current
is controlled by the design of the triac or electronic dimmer
selected.
The evaluation board was tested with a variety of
commercial dimmers. Figure 8 shows the dimming
performance with several triac and electronic dimmers.
Dimming control range varies by manufacturer, but a range
385
350
315
280
LED Current (mA)
245
210
Lutron LLSM−502
Clipsal KB31RD400
MK SX8501
Clipsal 32V500
Alombard 741021
Legrande Celiane
Clipsal 32E450UD
Clipsal 32E450LM
175
140
105
70
35
0
0
20
40
60
80
100
Conduction Angle (degrees)
120
Figure 8. Performance of Evaluation Board with Various Line Dimmers
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140
160
NCL30000LED2GEVB
Table 4 lists commercial dimmers successfully tested
with the evaluation board. The load is 12 LEDs
(Vf = 37 Vdc) and nominal current is set for 350 mA.
Table 4. DIMMER COMPATIBILITY CHART
Manufacturer
Minimum Conduction Angle
(degrees)
Dimmer Model
Current at Minimum
Conduction Angle (mA)
Alombard
741021
20.7
7.2
Clipsal
KB31RD400
38.2
55.2
Clipsal
32E450LM
10.6
1
Clipsal
32E450UD
30.8
29.5
Clipsal
32V500
9.2
0
Legrande
999.58
18
23.8
Lutron
LLSM−502
27.4
25.7
MK
SX8501
41.8
74
Conclusion
Additional Application Information and Tools
The NCL30000LED2GEVB is a versatile dimmercompatible LED driver. This board provides rapid
assessment of capabilities and serves as a basis for LED
driver solutions. Smooth flicker-free dimming performance
is demonstrated with a wide variety of commercially
available dimmers. Full 350 mA LED current is provided at
maximum dimmer setting. High power factor and high
efficiency provide a cost effective solution for a dimmer
compatible LED driver.
The
NCL30000LED2GEVB
evaluation
board,
NCL30000 datasheet, AND8451 Power Stage Design
Guidelines, Microsoft Excel Design Spreadsheet, and
AND8448 TRIAC Dimming application note are available
at www.onsemi.com.
Microsoft and Excel are registered trademarks of Microsoft Corporation.
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are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,
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limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications
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EVBUM2100/D